Modified variometer



v Oct. 11, 1949. GWFYLER 2,484,561

MODIFIED VARIOMETER Filed March 26, 1948 Ihventor:

George WFyIe zzflzk 0% H is Atcbrney.

Patented Oct. 11,1949

MODIFIED VARIOMETER George W. Fyler, Lombard, 111., assignor to General Electric Company, a corporation of New York Application March26, 1948, Serial No. 17,311

3 Claims. (Cl. 171-242) This invention relates to inductance coilsof the variometer type, and more particularly to such coils, suitable for providing tuning means for high frequency circuits, wherein the distributed capacity of the coils is reduced to a minimum.

One of the problems encountered in the design of television and radio receivers is that of providing suitable tuning means in the radio frequency amplifying stages and oscillator in such receivers. It is required that the radio frequency stages and oscillator be not only tuned through a frequency band, but also tuned to a plurality of such bands. This tuning is usually accomplished by providing a series of coils, each band being tuned by two or more separate coils and a switching arrangement to selectively switch the coils into the circuit, and to additionally provide tuning means such as variable capacitors, and

the like, for effecting Vernier tuning within a selected band of frequencies. Another'means is the well known type of variable inductance tuner which consists of a number of fixed coils with mechanically coupled sliding contacts engaging the turns in the respective coils.

It is an object of this invention to provide a variable inductance of the variometer type which is so constructed that the distributed capacity is low enough so that the variable inductance readily lends itself to utilization in the abovementioned types of radio frequency amplifying circuits.

It is a further object of this invention to provide a tuning arrangement for high frequency circuits which is relatively inexpensive and simple in construction, in comparison with similar types of known tuning arrangements.

Yet a further object of this invention is to provide a high frequency tuning arrangement which may be varied easily and rapidly throughout a wide range of frequencies.

Yet another object of this invention is to provide an improved variable inductance of the variometer type which may be utilized for tuning high frequency circuits and wherein the tuning may be effected silently without the accompanimerit of objectionable noise signals.

A still further object of this invention is to provide such a high frequency tuning arrangement which is variable throughout a wide range of frequencics and in which the rate of frequency variation within the range is substantially constant and the usual sharp tuning variation at the higher frequencies is obviated.

It is contemplated in the present invention to provide a tuning arrangement suitable for tuning the radio frequency stages and oscillator of a television or radio receiver which comprises a variometer of a modified form. A variometer usually consists of two coils in series with the mutual inductance between these coils either aiding or opposing. However variometers can also be made with the coils connected in parallel. The latter arrangement appears to be more desirable in order to overcome the rather high distibuted capacity of the series type variometer. In order to further reduce this stray capacity, it is proposed in the present invention to provide a series of one-turn variometers, each consisting of two sets of coils, and each coil being wound in the form of a figure 8 instead of a circle. The two figure as may then be rotated about the common axis so that the coil lobes either increase or decrease the over-all inductance.

The features of this invention which are believed to be new are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the accompanying drawing wherein Fig. 1 shows one form of a modified variometer constructed in accordance with the present invention, Fig. 2 shows a further modification of the variometer embodying the present invention.

Referring now to the drawing, Fig. 1 shows a modified form of variometer which is constructed in accordance with the present invention,

This variometer comprises a movable coil I which is made up of a desired number of turns and is adapted to be rotated about the axis of shaft 2. The turns of coil 1 are each wound in the form of a figure 8 and mounted on shaft 2 as shown, these turns being connected in series in the usual manner. Concentrically to shaft 2 there is mounted a further member 3 which is fixed and has a series of axial slots formed therein as shown, thus allowing axial movement of the coil l with respect to shaft 3. Mounted on memher 3 is a further coil 4 which is made up of a number of turns, as shown. These turns similarly have the shape of a figure 8 and are carried on member 3 in such a manner that rotation of shaft 2 varies the axial relation between the coil I and coil 4. The fixed and movable coils are connected in parallel and signals may be applied thereto by way of terminals'5.

It is apparent that when the movable coil is rotated about the axis of shaft 2 the figure 8 turns comprising this coil may be given any desired axial relationship with respect to the turns which make up the fixed coil and hence either increase or decrease the over-all inductance of the arrangement.

A device of the above construction formed by winding coils l and 4 of number 24 enamel covered wire was found to have a maximum inductance of 1 microhenry, by winding the two coils of number 24 enamel wire. After winding, the coils were separated slightly so that interleaving of the turns was possible in the two positions of maximum and minimum inductance. Using a Q meter it was determined that a tuning range of 2/1 in frequency could be obtained. This frequency variation is suflicient to cover the lower frequency television range. The higher frequency television range, which requires a smaller percentage change of inductance may be covered by employing a parallel padding inductance. Alternatively another smaller variometer coil may be employed, if preferred.

One of the features of my improved variometer construction is that cancellation and addition of mutual inductance between the two figure 8 coils is distributed along the length of the coils so that the high potential end does not come in close proximity "to the low potential end of the coil as 'in the usual type of yariometer.

"Fig. 2 illustrates a modification of the variometer of Fig. 1, which is similar in most respects to that of Fig. 1, and wherein like numerals are used to designate like components. The variometerin Fig. 'Zdiffers from that of Fig. 1 in that the various connections to the turns of the coils are brought out in the outside circumference thereof, as opposed to the arrangement of Fig. 1 which uses the axis of the device for these connections. This latter arrangement may prove to be more convenient in some instances.

This invention therefore provides a modified type of variometer having negligible distributed capacity and which may be used to tune radio frequency amplifying stages of television receiving systems. This type of coil may also be used either in a superheterodyne type of'radio receiver or with staggered tuning in successive radio frequency amplifier stages. Small series or shunt padding inductances maybe required in order to obtainthe desired band width in such a staggertuned radio frequency amplifier.

While certain specific embodiments have been shown and described, it will, of course, be understood that various modifications may be made without departing from the invention. The appended claims are therefore intended to cover any such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A variable inductance of the varlometer type including a pair of coils movable with respect to each other, wherein each of said coils comprises a plurality of spaced turns so arranged that the individual turns of one of said coils interleave respective adjacent turns of the other of said coils and wherein each individual turn comprises a plurality of lobes oppositely disposed with respect to a common axis and lying substantially in the same plane, and means for varying the position of one of said coils with respect to the other to alter the "mutual inductance therebetween.

2. A variable inductance of the variometer type including a pair of -.coils movable with respect to each other, respective supporting members for each of said coils, each of said coils comprising a plurality of spaced figure 8 shaped turns supported at the center on "said respective supporting members, said coils being so arranged that the individual turns of one .of said coils interleavenespective turns of the other of said coils,-.and menu for varying the position of one of said'co'ils respect to the other of said coils to alter the mutual inductance therebetween.

3. A variable inductancemf the xlzriometer'izype including a pair of coils movable withrespectto each other, respective supporting'members aforsupporting said coils, said supporting members being concentric (me to the other, said coils each having .a plurality of longitudinally spaced figure 8 shaped turns supported at the center on said respective supporting members, said coils being so arranged that the individual turns of one or said coils interleave respective turns .of the other .of said coils, and means for rotating one of wsaidsupporting members with respect to the other of said suppmting members to change the .axial position or one at said coils with respect to the other and hence the mutual inductance therebetween.

GEORGE REFERENCES CITED The following references are of record in the file of this patent:

STATES PATENTS Number Name Date 1,131,187 Von Arco et a1 'Mar. 9, 1915 1,445,242 Shackelton I'eb. 13, 1923 1,465,546 Donle Apr. 21, 1923 

